This invention relates to a body made of a doped semiconductor material of at least one type of conduction, having a mean free path length for free charge carriers in the semiconductor material and at least one area where the mean free path length for free charge carriers in the semiconductor material is reduced for the free charge carriers relative to a mean free path length of the semiconductor material.
A body of the aforementioned type is proposed in the older German Patent Application 10030381.1 (2000 P 12486), which was not published previously, the contents of which are part of the disclosure content of the present patent application.
With this proposed body, the doped semiconductor material has different types of doping and also has:
a junction between one type of conduction and the opposite type of conduction from this type of conduction,
a mean free path length for free charge carriers in the semiconductor material for each type of conduction, and
for one of the two types of conduction, it has a region in which there is a mean free path length for the free charge carriers in the semiconductor material which is reduced relative to the mean free path length for the free charge carriers of the semiconductor material of this type of conduction.
The area of reduced mean free path length for the free charge carriers in the semiconductor material leads in general to better electrical properties of the body of semiconductor material. Thus, in the case of the body already proposed, a high electric breakdown strength is achieved due to this area.
The object of this invention is to provide a body of the type defined in the preamble which has even better electric properties.
This object can be achieved by a body of doped semiconductor material of at least one conduction type, which has a mean free path length for free charge carriers in the semiconductor material and has at least one area in which there is a mean free path length for the free charge carriers in the semiconductor material, this mean free path length being reduced relative to a mean free path length of the semiconductor material for the free charge carriers, whereby the area of reduced mean free path length has sections which follow one another in at least one certain direction and between which there is at least one region in which a greater mean free path length prevails relative to the reduced mean free path length for the free charge carriers in the semiconductor material.
It is essential with this embodiment that the area of reduced mean free path length has sections which follow one another in at least one certain direction and between which there is at least one region for which free charge carriers are predominant in the semiconductor material.
Accordingly, with the body according to this invention, the area of reduced mean free path length is not continuous, as is the case with the body proposed in the past, but instead is interrupted by at least one region having a greater mean free path length relative to this path length. Therefore, in the area of reduced mean free path length, production of charge carriers by ionization due to collision is hindered by the reduced free path length of the charge carriers.
In the region(s) in which the greater mean free path length for the free charge carriers in the semiconductor material is predominant relative to the reduced mean free path length, this is accomplished by the geometry of each region. The charge carriers need a certain path length to be able to absorb enough energy on the basis of this so that they can themselves generate additional charge carriers by ionization due to collision. If this path length is kept small, then these charge carriers cannot take up enough energy.
In the case of the body according to this invention, measures are taken to ensure to advantage not only that an electric current flows in an area of reduced mean free path length but also that the current flows in at least one region where the mean free path length is greater than the reduced mean free path length.
Therefore, with the body according to this invention, it is possible to advantage to implement a component with a body made of a semiconductor material in which the free path length of the charge carriers need not be reduced everywhere that a high electric field strength prevails.
With the body according to this invention, its electric conduction property is improved in comparison with that of the body having the continuous area of reduced mean free path length as was customary in the past.
An advantageous embodiment of the body according to this invention is designed such that there is a distance between adjacent regions having a greater mean free path length relative to the reduced mean free path length, these regions being separated by a section of the area of reduced mean free path length which determines this distance, which depends on the absolute value of an electric field strength generated by applying a certain electric voltage to the body in the semiconductor material, such that this distance decreases at a location of a lower absolute value and increases at a location of a greater absolute value. For example, this may mean that such regions are arranged in a greater density in areas where the absolute value of the electric field strength is lower, and such regions are arranged in a lower density in areas where the absolute value of the electric field strength is higher.
Another advantageous embodiment of the body according to this invention is designed so that a distance between adjacent sections of the area of reduced mean free path length, separated by a region with a greater mean free path length relative to the reduced mean free path length, depends on the absolute value of an electric field strength generated by applying a certain electric voltage to the body in the semiconductor material such that this distance is greater at a location of a smaller absolute value and is smaller at a location of a greater absolute value. For example, this may mean that such sections are arranged in a greater density in areas where the absolute value of the electric field strength is greater and they are arranged in a lower density in areas where the absolute value of the electric field strength is lower.
These two embodiments may be combined.
In a preferred and advantageous manner, the relative greater mean free path length of a region is equal to the mean free path length of the doped semiconductor material of the one type of conduction outside of the area of reduced mean free path length.
An especially preferred and advantageous embodiment of the body according to this invention is designed like the body already proposed, so that the doped semiconductor material has different types of doping and
has at least one junction between one type of conduction and a type of conduction opposite this former type of conduction,
has a mean free path length for free charge carriers in the semiconductor material for each type of conduction and
has for at least one of the two types of conduction an area in which there is mean free path length for the free charge carriers in the semiconductor material which is reduced relative to the mean free path length for the free charge carriers of the semiconductor material of this one type of conduction,
whereby the area of reduced mean free path length has at least two sections which follow one another in the direction perpendicular to a surface in which the junction extends and between which there is a region where a greater mean free path length for the free charge carriers in the semiconductor material prevails relative to the reduced mean free path length, and/or
whereby the area of reduced mean free path length has as least two sections which follow one another in at least one direction parallel to the surface in which the junction extends and between which there is a region in which a greater mean free path length for the free charge carriers in the semiconductor material prevails relative to the reduced mean free path length.
On the one hand, a high blocking voltage may be applied at the junction in an advantageous embodiment, while on the other hand, the electric conduction property of the junction is improved.
In a preferred and advantageous design of the advantageous embodiment, there is a distance between adjacent regions which are separated by a section of the area of reduced mean free path length, this distance depending on the absolute value of an electric field strength generated by applying a certain electric blocking voltage to the junction in the semiconductor material such that this distance is greater at a location of a smaller absolute value and is smaller at a location of a greater absolute value.
With the body design according to this invention, in particular in its advantage embodiment, a high voltage component can be implemented to advantage with a body of a semiconductor material, which has low forward power losses and switching losses but on the other hand also has a small component volume. It is thus possible to implement both a high voltage component with a small volume as well as a high-voltage IC (HVIC) of extremely high integration.
High-voltage components are implemented today essentially through the choice of the lowest possible base doping in an n-doped base of its body of semiconductor material. However, there are limits to this measure from the standpoint of the lowest possible total power loss in the component, because reducing the base doping usually also results in an increased component thickness. HVICs are implemented either in junction isolation technology (JI technology) or in dielectric isolation technology (DI technology). Both technologies require a xe2x80x9cthickxe2x80x9d drift zone to be able to accommodate the required blocking voltage.
With the body design according to this invention, it is possible to implement, for example, an electric resistor in addition to a thyristor, a transistor or a power MOSFET HVIC.